It is known and widespread that rotor blade rows of turbines of gas turbines have, at the upper end of the blade airfoils, what is termed a shroud.
EP 1 965 033 A2 shows a rotor blade outer air seal segment of a turbine machine, which comprises a body with a base part. The base part has a transverse concave internal diameter surface, a front end, a rear end and first and second peripheral edges. The body comprises at least one mounting hook. At least one cover plate is attached to the body, so as to define at least one cavity. The cover plate comprises multiple feed-through holes. Multiple outlet holes extend through the base part to the internal diameter surface. At least the base part or the cover plate has a projection which protrudes into the cavity, so as to form a partial partition which separates a front cavity part from a rear cavity part.
An impingement cooling structure, for cooling hot walls of a turbine shroud and a turbine end wall, is known from EP 1 990 507 A1. The impingement cooling structure comprises multiple shroud elements arranged in a circumferential direction to form an annular shroud which encloses a hot gas stream, and a shroud cover which is mounted on radial outer surfaces of the shroud elements, so as to form a cavity therebetween. The shroud cover has a first impingement cooling hole which is connected to the cavity and which allows cooling air to be injected into the cavity such that an internal surface of the cavity is cooled by impingement. Each shroud element has a perforated fin. The perforated fin divides the cavity into multiple sub-cavities. Furthermore, the perforated fin comprises a second impingement cooling hole which allows the cooling air to flow through the first impingement cooling hole so as to be injected obliquely in the direction of a bottom surface of an adjoining sub-cavity.
US 2011/044805 A1 discloses a cooling system for a ring segment of a gas turbine. The cooling system comprises an impingement plate which has multiple small holes, a cooling space which is enclosed by the impingement plate and a main body of a segment body, a first cavity which is arranged in a downstream end position of the segment body in the flow direction of the combustion gas, such that it stands perpendicular to an axial direction of a rotation shaft, a first cooling duct which is connected to the cooling space and the first cavity, and a second cooling duct which is connected to the first cavity and a combustion chamber, which is arranged in a downstream end position of the segment body in the flow direction of the combustion gas.
WO 2008/128876 A1 relates to a stator heat shield for a gas turbine and to a gas turbine equipped with such a stator heat shield. The stator heat shield comprises an outer side which, in the installed state, is oriented toward a hot gas path of the gas turbine, an inner side which is oriented away from the outer side, multiple ribs which are formed on the inner side and which, in the installed state, extend axially with respect to a rotation axis of a rotor of the gas turbine and are spaced apart from one another in the circumferential direction, at least one impingement plate which is arranged on the inner side and which rests against the ribs, at least one groove which is formed in an end side bounding the stator heat shield in the circumferential direction and into which at least one sealing element can be fitted, and multiple bores which in each case at one end open onto the end side, spaced apart from the groove in the direction toward the outer side, and at the other end open onto the inner side, and which are spaced apart from one another in the axial direction.
US 2004/047725 A1 shows a ring segment of an annular form which is arranged around the outer circumference of rotor blades of a gas turbine. The ring segment comprises a blade ring, a main shaft and rotor blades with multiple individual units which define an annular form in that they are arranged around the circumferential direction of the main shaft and are arranged such that their inner peripheral surface is guided at a constant distance from the tips of the rotor blades. In that context, the individual units form depressions, which extend along the axial direction of the main shaft of the turbine, such that they are opposite one another. The ring segment also comprises a sealing plate, which is fitted in each opposing pair of the depressions such that the adjoining pairs of the individual units are connected to one another, and contact surfaces, which are formed at positions radially further inward than the sealing plates and extend in the axial direction and the circumferential direction and are in contact with one another.
Such shrouds make it necessary, during work on the rotor blade row which for example takes place for maintenance or testing purposes, to perform what is referred to as a cover lift, that is to say lifting the entire upper casing part in order to exchange ring segments which are arranged around the rotor blades. A cover lift is very onerous.